coehorn golfball mortar birthday gift

[neilert]

I'm a new member, and this is my first post-  Your forum is great.

Dad's birthday is coming up in July, and I'm building him a golf ball mortar.
It is inspired by CU's plans- thank you for posting them CU!!!! I'll send photos to you when it's done as requested in your post.

I've never built a cannon or a mortar, so I'll need everyone's help with the details.

Here's a photo of the first chips cut from a 4" dia. x 7 1/8" long 1018 steel rod.

[Cat Whisperer]

neilert-

WELCOME to the board!

Looks like a great start!  Good choice of metal too.

Keep plenty of stock all around the powder chamber (what size are you going to do?).

A future heirloom to be sure.

[neilert]

"Keep plenty of stock all around the powder chamber (what size are you going to do?)."


CU Cannon's plans show a 1.73x 3 15/16" deep bore for the golf ball, I'm not sure what scale that is compared to the original coehorn.
I may delete the mechanical fasteners at the trunnion and use tig welds-  any thoughts?

[GGaskill]

I may delete the mechanical fasteners at the trunnion and use tig welds-  any thoughts?

I like TIG welding.  And don't do the round/tapered part of the breech until you have drilled the bore or you won't be able to hold it.

[CU_Cannon]

It looks like you have a great start.

I made the plans up before I had a set of ordinance drawings for a true scale model.  The mortar came out great but now that I know the correct proportions I prefer the scale ones better. 

I attached the trunnion with screws because of the alloy I used and the lack of welding equipment.  Welding would be better in this application.

[neilert]

CU-
Thank you again for these plans.  Have you updated them now that you have updated measurements?
I would really appreciate them if they are available.  I'll plan on tig welding the trunnion.  Tonight I'm boring it.  The boring operation will take quite a while because my largest drill bit is only 5/8" dia.

It looks difficult to place the radius in the combustion chamber portion.  Does it have to be a radius, or is there another solution?

Thank you for everyones help-  Neil

[Cat Whisperer]

If you have a 1" diameter powder chamber, keep at least 1" of steel around the sides AND underneath.

1018 is easily weldable without the complications encountered with, say, 4130 or 4140.  Remember that the area near the weld is going to be stressed - so allow for some material between it and the powder chamber.

[neilert]

Here it is with the major diameter (1.73") bored.  I went ahead and turned the breech radius, and I have not yet bored the powder chamber, thinking that I would mill it out somehow.  Should I just use a ball end mill?  It looks like everyone has a can of black powder for scale reference, but I don't have any yet, so the cigar is for scale.

[Cat Whisperer]

Boring on the lathe is the easiest, as when you do the bore.

BUT, now you'll have the same issue with doing on the mill - that of clamping.

It's looking good!

If you do use a ball end-mill (they do work well) you might want to drill out as much as you can first - the end mill may or may not clear the chips (depends on the design of the end-mill).

[neilert]

Here's the photos of the finished mortar-  I used white oak that was left over from another project, with linseed oil finish (Dad's favorite wood and finish).  Instead of the end mill for the powder chamber, I ended up making a form tool with a 1/2" HSS blank welded to a steel boring bar.  It worked, but had some chatter.  The finish on the steel is a Caswell plating black oxide finish.  It's my first attempt at the black oxide process, and it worked well.  I ordered the fuse from cannonfuse.com and it arrived fast.  The black powder was in stock at Cabela's kansas city store.  The hardware and thru bolts are custom, machined out of brass.  I'll take it back to Dad's farm next weekend to give it to him and shoot some golf balls.  Thank you for all of your help, reference photos and drawings, and advice.  I'm hooked.  It's time to build a howitzer next. 

[neilert]

more photos.....

[neilert]

top view-

[Rickk]

way cool 

[lance]

really nice work, now that's a birthday gift that won't be stuffed in the closet.